Recently, significant advances have been obtained to meet the need for the Ultra Large Scale Integrated (ULSI) circuits. Semiconductor integrated circuits currently being manufactured follow ultra high density design rules and circuits manufactured in the near future will follow even smaller design rules. Chip yield on the processed silicon wafer becomes an important topic when electronic devices are shrunk today. The operation voltage and power are decreased, thus, the tolerance of defect and error in device also been decreased significantly.
Chemical vapor deposition (CVD) for dielectrics is an importance process in the modern semiconductor process, because of good ability of step coverage. In generally, the dielectrics include silicon dioxide (SiO.sub.2), silicon nitride (Si.sub.3 N.sub.4), phosphosilicate glass (PSG), and borophosphosilicate glass (BPSG). BPSG often be used as pre-metal dielectric, which has good planarization characteristics after performing a thermal flow process. Therefore, BPSG is widely used as a pre-metal insulating layer in the manufacture of semiconductor devices.
A BPSG film is deposited generally by chemical vapor deposition (CVD) process. The BPSG film is formed by introducing a tetraethoxysilane (TEOS), a phosphorus containing source, a boron containing source into a processing chamber along with the oxygen containing source. An example of phosphorus containing source is tri-methyl-phosphate (TMPO). An example of boron containing source is tri-methyl-borate (TMB). TEOS, TMPO, and TMB are liquid in normal atmospheric that is a need to heat for increasing saturated vapor pressure. Helium gas is used as carrier gas for increasing the vapor partial pressure of liquid reactants.
Please refer to FIG. 1, which shows a liquid injection valve of a conventional chemical vapor deposition system, wherein a heater 12 is used to maintain the gas lines at selected temperature. The process liquid sources 14 are transferred to liquid injection valve 10 passing the liquid lines 16. The liquid sources are vaporized and delivered to a processing chamber 20 by helium carrier gas 18. The liquid injection valve provides greater control of the volume of reactant sources. However, the pore and dimension of pass line in the liquid injection valve are tiny. There are at least three valves between liquid lines and the processing chamber. When the deposition process is complete, residuals of the reactants always are remained in the valve system. The residuals of the reactants cause the concentrations of boron and phosphorus unstable at next deposition process. The Yield of BPSG film will be decreased.
Please refer to FIG. 2, which shows a cross-sectional view of a semiconductor wafer with BPSG film generating bubble defects after high temperature flow. A plurality of devices 24 is formed on the semiconductor substrate 22. A dielectric layer (not labeled) is then formed over the devices and substrate for isolation. Before metallization process, TEOS/O3, TMB, TMPO are reactants for depositing BPTEOS film 26 by atmospheric pressure chemical vapor deposition (APCVD) for planarizing topography. The thin dielectric layer (not labeled) is an interlayer of the BPTEOS film for protecting the active areas of devices.
As described above, there is a need to perform a thermal flow at 850 to 900.degree. C. for increasing planarization of topography. Referring to FIG. 2, the BPTEOS film by conventional deposition process has unstable concentrations of boron and phosphorus. The phosphorus in the BPTEOS has good gettering moisture characteristic. It is easy to form bubble defects in BPTEOS film after thermal flow, especially containing high concentration of phosphorus. It is easy to form crystal defects in BPTEOS film after thermal flow, especially containing high concentration of boron.
Therefore, it is a need to disclose a method for avoiding the concentrations of boron and phosphorus unstable and preventing bubble defects in BPSG film.